Field of the Invention
The present invention relates to a radar device and a velocity calculation method with which Doppler velocity can be calculated more accurately.
Background Information
A radar device for detecting the velocity of a target, such as rain or clouds, transmits a plurality of pulse signals and calculates the velocity from the amount of phase rotation of an echo signal reflected by the target. This radar device is only able to calculate a velocity at which the Doppler frequency is less than the pulse repetition frequency (PRF), and if the target velocity is high, the Doppler frequency between pulses may exceed the PRF, which is the observation limit. When this happens, so-called “folding” occurs, in which the calculated velocity is observed as being lower than the actual velocity, and this makes it impossible to calculate the velocity accurately.
To regard to this, Non-Patent Literature 1 (H. Adachi and Y. Sato, “Doppler Weather Radar,” Toshiba Review, Vol. 55, No. 5 (2000), pp. 27-30) has disclosed a method with which the actual velocity can be calculated even if folding occurs. With this method, pulse signals are alternately transmitted at two pulse repetition frequencies. The number of folds is determined from the difference in velocity obtained at the two pulse repetition frequencies, and the corrected velocity is calculated based on this number of folds.